Standard PVC grades for thermoplastic processing are generally based on the suspension process (S-PVC). The K values start at 57 and extend up to 73, covering almost all large-volume applications. The lower K values 57 to 60 are used for hard films and thin-wall profiles, as well as for injection molding; the higher K values are used in the pipe and profiles segments, which still dominate the thermoplastic applications in terms of volume. K values of 70 and higher with corresponding grain morphology for absorbing plasticizers are mainly used in flexible products. Because of the increasing cost pressure in all these applications, processors try to use ever higher quantities of fillers or recyclate. However, there are qualitative limits to the use of fillers, which affect the mechanical end product properties and welding or the conveying properties of the dry blend.
The aforementioned standard grades are complemented with higher polymeric products with K values of about 80, which are particularly used in the flexible PVC area, if high mechanical specifications are required. Examples of this are hoses and cables. In the cable industry, the trend towards e-mobility is setting new challenges, since the number of electrical cables in the vehicle is growing strongly, but it must be reconciled with demands for weight reduction and space saving (Fig. 1). A step further is taken by special products with K values of 93 to 100, which are mainly used for dynamic window seals. Special grades are suitable for absorbing particularly large quantities of plasticizer of 180 parts and more, which allow Shore A hardness of 35 and below to be achieved.
For special requirements, a large assortment of new long-chain or polymeric plasticizers is now available, with relatively low migration. This can be further reduced by the use of suitable two-phase graft copolymers based on butyl acrylate and vinyl chloride. Since these products have their own soft phase, they have a lower plasticizer requirement per se, which is even more effectively bound in the polymer matrix. As a result very high quality, durable flexible PVC products are obtained, with tactile properties similar to natural rubber, but which are superior as regards their weathering resistance, processing characteristics and the possibilities for pigmentation. These graft copolymers are enhanced versions of PVC additives that were originally developed for the impact modification of rigid profiles. The soft acrylate phase absorbs the impact energy in the hard PVC matrix and converts it into heat. These impact modifiers are currently used as a 50 % concentrate or, with approximately 7 % acrylate, as base resin, usually for window profile applications. These applications have the common feature that, due to the very uniform phase distribution and the absence of inactive sheathing of the soft phase, they are highly effective and have very good processing properties.